The invention relates to a unit consisting of a proximity switch and a cable terminal part and a process for its manufacture.
The prior art discloses different possibilities for joints or terminals of cables which are detachable and undetachable from a proximity switch. Plug connections, therefore cable joints, which are made using plug connectors which can be connected to the terminals of proximity switches are known for example from German patents 195 28 678 and 44 10 023. Another detachable cable joint, specifically a screw-type terminal, is known from German patent 195 29 181. Relating to nondetachable cable terminals on proximity switches, reference is made by way of example to the German patent 42 25 267 in which a housing termination consisting of hot-melt cement is described, through which the cables which are connected directly to the electronics in the proximity switch are routed out of the proximity switch.
Both the detachable joints of cables on proximity switches which are known from the prior art as well as the nondetachable cable terminals for proximity switches which are known from the prior art have a series of defects. The detachable joints generally require a relatively large amount of space. Since however recently the trend has been to smaller and smaller proximity switches, only little space is available for one such detachable joint. In designs with plug connectors it is moreover disadvantageous that they are much more expensive to manufacture than proximity switches to which the cables are directly connected.
In the last two decades especially in inductive proximity switches it has been possible to further increase the operating distance at the same outside diameter of the coil used for the inductive proximity switch. This means that at a uniform operating distance the outside diameter of the proximity switch which is essentially dictated by the coil diameter has been reduced. This is advantageous to the user, but entails problems in connectorization mainly in smaller devices, which are made for example in thread sizes M 6 to M 12, i.e. cable or plug terminal technology, since the maximum plug diameter in cylindrical proximity switches generally will not be greater than the threaded or smooth sleeve diameter of the proximity switch in order to enable any installation in walls of different thickness.
In proximity switches with a nondetachable cable joint, either the cable is permanently connected to the electronics and the entire unit after adjustment is inserted into the housing of the proximity switch and potted or the electronics in the housing of the proximity switch is connected via flexible wires to the cable or plug, and only after final testing are the cables and plugs connected undetachably and mechanically permanently to the housing, for example by potting. These types of direct connection enable the shortest overall lengths, due to the long wires however a large amount of space is necessary.
Since the users of proximity switches for one type of a proximity switch at a time ask for cable colors, cable materials and cable sizes which are different from one another, the diversity of types of proximity switches provided with cables is very great; this leads to the fact that the warehousing costs for storage of all conceivable types of proximity switches are considerable.
Proceeding from the above explained prior art, the object of the invention is to devise a technically and economically especially favorable unit consisting of a proximity switch and a cable terminal part and a corresponding process for its manufacture.
The unit consisting of a proximity switch and a cable terminal part in which the aforementioned object is achieved is characterized in that the proximity switch has an outside housing and an insulation part, the insulation part is provided on the end face of the outside housing and has a terminal element with terminals which leads to the outside, the terminals of the terminal element which lead to the outside are made as terminal sockets, the cable terminal part has a cable and a connecting part, the cable is attached in the connecting part, the connecting part is attached to the insulation part and the ends of the wires of the cables are connected in an electrically conductive manner to the terminal sockets of the terminal element.
With the unit as claimed in the invention consisting of a proximity switch on the one hand and a cable terminal part on the other, the result is that the proximity switch can be completely finished, can be checked based on the electrical terminals which are present in the form of the terminal sockets and can then be stored. Connectorization with the cable required by the user takes place then using the cable terminal part which consists essentially of connecting part which fits the proximity switch and the cable which is wanted by the user and which is attached in it. The proximity switch and the cable terminal part can be quickly joined together, easily and reliably.
Basically a host of dimensions and forms are possible for the outside housing and the insulation part of the proximity switch and for the cable terminal part.
According to one preferred development of the invention it is provided that the maximum diameter of the cable terminal part is less than or equal to the maximum diameter of the insulation part and the maximum diameter of the insulation part is less than or equal to the maximum inside diameter of the outside housing. If the maximum diameters of the cable terminal part, the insulation part and the outside housing are chosen as indicated, the proximity switch can be inserted as far as desired into the hole which is provided for its attachment. Preferably it is provided for attachment of the proximity switch in the hole that the proximity switch has an outside thread with which it can be screwed into the inside thread which is provided in the hole.
In order to preclude pin confusion or polarity reversal when the proximity switch is joined to the cable terminal part, according to one preferred development of the invention it is provided that the insulation part and the cable terminal part each have codes which correspond to one another and which indicate for the joining of the proximity switch and cable terminal part the correct alignment of the cable terminal part to the insulation part, therefore that alignment of the two components to one another in which the desired contact-making of the wires of the cable which has been attached in the connecting part of the cable terminal part with the terminal sockets of the proximity switch is achieved. Alternatively or additionally, it is preferably provided that the insulation part and the cable terminal part each have a form such that they can be joined exclusively in the correct alignment of the cable terminal part to the insulation part. Before final attachment of the cable terminal part to the insulation part in the manufacture of the unit as claimed in the invention, twisting of these two components to one another is therefore no longer possible; this further reduces possible problems in connectorization.
Different techniques are possible for connecting or attaching the ends of the wires of the cable to the terminal sockets of the terminal element. For example, the terminal sockets can be slotted or can be made at least partially elastic so that the stripped ends of the wires of the cable which are then preferably tin-coated and/or bear at least partially conductive sleeves into which the terminal sockets can be inserted and as a result of the spring action of the terminal sockets hold easily and securely in them and have good contact to them. According to one preferred development of the invention it is however alternatively provided that the terminal sockets are designed to accommodate connecting means. Preferably solder or conductive cement, especially conductive silver cement, is used as the connecting means. The stripped ends of the wires of the cable then project into the terminal sockets, are preferably likewise tin-coated and/or provided at least partially with conductive sleeves and are soldered or cemented in the terminal sockets.
To attach the insulation part in the outside housing likewise different techniques can be used. According to one preferred development of the invention it is however provided that the insulation part is attached in the outside housing by impressing the housing. To attach the insulation part in the outside housing then techniques are used which are described for example in the German utility model 299 01 548. To ensure reliable sealing of the proximity switch, it is provided preferably in addition or alternatively that between the insulation part and the housing there is a seal, preferably an elastomer O-ring.
If the insulation part is made of an insulating material, the terminal element can be made very simply, specifically special insulation is not necessary for the terminal element. In particular, it is preferable to make the insulation part in plastic. The outside housing can also consist of different materials, especially metal or plastic. If the outside housing is likewise made in plastic, the insulation part can be inserted securely into the outside housing, forming a seal, by means of ultrasonic welding.
If the insulation part is made transparent according to one preferred development of the invention, in the proximity switch there can be a display-LED which is visible through a viewing hole in the outside housing and which is useful to the user for recognizing the operating states of the proximity switch.
One especially simple connection when the cable terminal part is joined to the proximity switch is achieved when in the connecting part there is an alignment aid for alignment of the ends of the wires of the cable. Using one such alignment aid the cables are arranged such that they correspond to the terminal sockets in the insulation part in terms of position. One such alignment aid is preferably made by there being holes into which the ends of the wires of the cable are inserted in the lengthwise direction of the connecting part.
The cable terminal part can be attached to the proximity switch in different ways. According to one preferred development of the invention it is provided that the cable terminal part is connected to the outside housing by impressing the housing. Alternatively or additionally the cable terminal part can be cemented to the insulation part. If the cable terminal part and the insulation part are made of plastic, the two components can also be joined to one another also by means of ultrasonic welding.
Joining of the proximity switch to the cable terminal part is facilitated according to one preferred development of the invention by the insulation part or the outside housing forming a guide in the radially outer area for the cable terminal part. In doing so the length of the guide can be dimensioned such that in the manufacture of the unit when the proximity switch and the cable terminal part are joined the cable terminal part comes into contact with the guide before the ends of the wires of the cable reach the terminal sockets. Thus distortion and along with this possible faulty contact-making of the ends of the cable wires are reliably prevented.
The process as claimed in the invention for producing a unit consisting of a proximity switch which has an outside housing and an insulation part and of a cable terminal part which has a connecting part and a cable and with which the aforementioned object is achieved is characterized by the following steps, the indicated sequence not being mandatory:
connecting the outside housing and the insulation part,
providing the insulation part with a terminal element which runs through; its terminals which lead to the outside are made as terminal sockets,
attachment of the cable in the connecting part,
attachment of the cable terminal part to the insulation part and
electrically conductive connection of the ends of the wires of the cable to the terminal sockets of the terminal element.
The advantages which are achieved with the process as claimed in the invention have already been addressed above. In the described manner the connectorization of the proximity switch with the cables required by the user is facilitated, and it is not necessary to warehouse a large number of all possible combination types of proximity switches with the cables attached to them.
Preferred developments of the process as claimed in the invention result on the one hand from the above described preferred developments of the unit as claimed in the invention consisting of a proximity switch and a cable terminal part. In addition, the process as claimed in the invention finds one preferred development in that the stripped ends of the wires of the cable are attached by induction soldering in the terminal sockets which have a solder connecting means. This induction heating of the terminal sockets and thus of the solder provided in them is achieved by a coil around the transition of the cable terminal part to the insulation part, only the terminals sockets and the stripped ends of the wires of the cable being heated by the coil in the current-carrying state. In this preferred development of the process as claimed in the invention it can furthermore be provided that the stripped ends of the conductors of the cable are tin-coated and/or are provided at least partially with conductive sleeves before they are inserted into the terminal sockets. In this way reliable and secure contact-making is ensured.